1. Field of the Invention
This invention relates in general to methods and apparatus for joining pipe ends and in particular to methods and apparatus for joining pipe ends without the necessity of rotating the pipe or, where desired, with only a slight rotation of one pipe relative to the other.
2. Description of the Prior Art
There are a number of applications for joining pipe ends in which it would be desirable to join the ends without the necessity of rotating the respective pipes themselves. One example would be in the oil industry, and particularly in the area of offshore production. On a drilling rig, rotation of one pipe end relative to the other is typically accomplished either by use of a hydraulic power tong which requires a specialized crew to operate, or a more basic “rope technique” consisting of pulling on a soft rope from the drilling rig main winch capstan. Final make-up torque is achieved by using a mechanical tong. The maximum amount of rotation achieved in one stroke of such a mechanical tong/cathead chain assembly is approximately one-quarter to one-third of a turn without the necessity of having to reset the assembly by manual reverse rotation. Production pipelines, on the other hand, have often been welded together in the past.
A suitable push-together connection would have advantages in off shore applications, for example, by providing the ability of being able to make-up and disconnect underwater connections remotely.
Also, a push-together connection would be simple to implement and would eliminate costly welding operations which have become almost prohibitive in some situations due to the high hourly cost of offshore operations.
There are other applications where, for example in construction, oil and gas and mining, where a slight rotation of one or both of the pipes being joined may be acceptable. Such a connection system could have application for drive pipe, riser pipe, conduit and casing liners for oil and gas operations, for example.
One way that the oil industry has attempted to address the problem of creating a secure pipe connection, particularly in joining offshore casing and tubing, was by introducing a specialized generation of thread connectors using modified A.P.I. threads. These threaded connectors are still widely used today, for example, for dimensions below twenty-four inches, despite the general requirement of a minimum of two and one-half turns of rotation for make-up.
A threadless connector for large diameter casings has also been used in the past which was based upon a snap-ring linkage type mechanism. These “snap-ring” type connectors offer fast make-up but offer neither the low weight-to-capacity ratio, nor the integrity or price competitiveness of the threaded connector for a given capacity.
Another type connector featuring radial dogs was introduced to replace flange connections, in a mechanical configuration for drilling riser connections, and in a hydraulic configuration for wellhead connections. Recently, the use of dog type connectors has been extended to offshore platform anchoring pile connections, but its success has been limited by its high cost, due to the large number of parts and the relatively heavy section required in the design and manufacture of such a connector.
In addition to the oil industry, numerous other applications exist for joining tubular pipe ends. For example, tubular pipe connections are used in a variety of civil engineering applications, including their utilization in providing structural support in the construction field. One such use of tubular pipes can be found in the building of underground tunnels. More specifically, tubular pipes provide support to large underground tunnels that are typically used as roadways or other transportation means. The large scale construction of underground tunnels for transportation applications is presently underway in Europe, Japan and elsewhere.
In a typical procedure to construct an underground tunnel, a large pipe, or possibly several large pipes, is laid by a boring machine and forms the main tunnel. Next, a boring machine proceeds to lay relatively smaller curved pipes surrounding the main tunnel to provide additional structural support These small curved pipes are commonly constructed as 10 foot sections having, for example, a 32 inch outer diameter. It is then necessary to connect these individual sections to provide a single, lengthier curved pipe adjacent to the underground structure. The process is repeated, placing these connected pipe sections parallel to one another for the duration of the desired length along the main tunnel, creating in effect a “whalebone” configuration surrounding the main tunnel. The voids in and around the pipes will be subsequently filled with concrete. In an application such as an underground roadway that reaches upwards to 12 miles, somewhere on the order of 80,000 connections would be needed to couple the individual pipe sections together to provide enough support to adequately enlarge the surrounding area of the main pipe.
Various techniques have been provided at the present time for connecting these individual curved tunnel pipe sections where the pipe sections themselves cannot be rotated. As with the offshore oil industry, one technique presently used in many situations, is to join two or more of these pipe sections together by welding, either by hand welding or semi-automatic welding processes. Welding is a time consuming activity, at best. Also, there is the possibility of defects in the welds and poor workability of the resulting materials due to heating of the metal. In low temperatures, countermeasures such as the preheating are necessary. In general, a welding process can take somewhere from 2 to 5 hours to weld one connection for a tunnel pipe section, depending on the size or complexity of the connection. With this in mind, time constraints virtually eliminate the practicality of welding each coupling in large projects consisting of thousands of pipe sections of the type under consideration.
Another technique which has been proposed for joining pipe ends, where the pipes themselves cannot be rotated, is the use of the so-called “adhesion joint.” This method injects, for example, an acrylic adhesive into the clearance of the joint interval, after which a post-line tube is inserted. It is possible to carry out the construction in a shorter time than the welding method, but the adhesive may not be applied uniformly, resulting in compromised connections. The adhesives may be messy to apply and may not furnish the required strength for some connection applications.
U.S. Pat. No. 4,487,433, issued Dec. 11, 1984, to Miller, shows an anti-rotation coupling wherein similarly pitched and profiled, but oppositely threaded ends, are provided for two couplings incorporating an anti-rotation member such as a tongue and groove or a hole and dowel pin. The patent seems to be primarily concerned with keeping the pipes anti-rotational once the connection is assembled, however.
U.S. Pat. No. 4,846,508, issued Jul. 11, 1989, to Pallini, Jr. Et al., shows a tubular connector system for joining two pipe ends without the necessity of rotating the pipe ends. One pipe end is provided with an external thread and a second pipe end includes multiple thread lead entries. A special tubular connector is also provided which includes an internal thread at one end and internal multiple thread lead entries at the other end. The tubular connector is first threaded onto the first pipe. Next, the second pipe is stabbed into the second end of the tubular connector and the tubular connector is then rotated less than a single turn with respect to the second pipe to fully mate the tubular connector and the second pipe. It appears that the connector is screwed all the way in on a first pipe end and is then “backed-off” a slight amount as the second pipe end is screwed in (rotated less than a single turn). Even this slight amount of rotation would not be acceptable in many of the applications discussed above, however.
A need exists, therefore, for an improved method and apparatus for joining tubular pipe ends, which method does not require the rotation of one pipe section relative to another, or which requires only slight rotation of one of the pipes.